What is the role of the 4-tuple in identifying a TCP connection, and how can contentions be avoided?

• A. The 4-tuple identifies a single packet's data payload.
• B. The 4-tuple identifies the exact TCP connection (source IP, source port, destination IP, destination port); proper port assignment helps avoid contentions.
• C. The 4-tuple identifies the route path for the packet.
• D. The 4-tuple is used to determine the encryption algorithm.

Answer: (B)

The 4-tuple identifies the exact TCP connection and enables proper delivery by the receiving host. It consists of the source IP, source port, destination IP, and destination port. That combination lets the TCP stack know which particular connection a segment belongs to, so data is routed to the correct socket and the correct connection state is advanced.

To avoid contentions, each new connection should use a distinct source port (an ephemeral port chosen by the client). Even if two connections go from the same client to the same server and port, differing source ports produce different 4-tuples, keeping the connections separate and preventing mix-ups in demultiplexing. The destination port indicates which service on the server is being reached, while the source port distinguishes multiple concurrent connections to the same service.

The other ideas don’t fit: the 4-tuple isn’t about a single packet’s payload, it doesn’t encode a route, and it isn’t used to select an encryption algorithm.